a) Field of the Invention
The present invention relates to a system, apparatus and method for testing elongate objects, such as pipe, pipeline, as well as storage tank, etc., and is directed toward the problem of detecting corrosion, and/or defects, and/or other anomalies to the pipe or pipeline under conditions where access and/or visual or instrumental inspection of the pipe or pipeline is either limited, not possible, or impractical.
b) Background Art
In petroleum processing and petrochemical plants and other industrial environments, it is common to have numerous pipes extending between various locations in the plant, with these pipes carrying fluid or gas (e.g.,petroleum products), often under intensive heat and high pressure. Likewise, trans-continental and interstate oil/gas pipelines under even higher pressure extend hundreds and thousands miles.
Similarly, pipelines carry toxic and non-toxic wastes, and storage tanks store high pressure gas and other volatile petroleum products, etc. These pipes or pipelines are invariably made of steel and can have an inside diameter ranging anywhere from two to sixty inches, or even outside of this range. The exterior of these pipes or pipelines are often insulated, and shielded with the insulating and metallic shielding layers being as great as approximately 1/8 to 5 inches or more in thickness, or outside of this range. Moreover, these pipes or pipelines are interconnected by joints, elbow joints, flanges, etc., while their geometrical configurations of the layouts are complex.
For a number of reasons, (safety, environmental potential hazards, avoiding costly shut-downs, etc.), the integrity of these pipes or pipelines must be preserved. Corrosion and/or defects in the pipe or pipeline can occur for a number of reasons. One is that moisture condensates can collect between the insulating layers and the pipe or pipeline, thus causing corrosion (i.e., rust). Visual inspection of the steel pipe that is encapsulated in insulation is not possible unless the layers of insulation and shielding are removed, and then replaced. This is expensive and time consuming, and as a practical matter it would be economically unfeasible to accomplish the inspections with reasonable frequency.
U.S. Pat. No. 4,970,467, Burnett, issued on Nov. 13, 1990. The method and apparatus in this patent are directed toward detection of corrosion in pipes and pipelines. Two pulses are transmitted into the pipe to travel toward one another, and these pulses intersect at an intermediate location. If there is corrosion at the location of the intersection, then this affects the pulses in a way which would be indicative of corrosion, and the resulting wave forms would differ from those which would result where the intersection of the pulses is at an uncorroded area of the pipe. By timing the transmission of the two pulses and shifting the transmitting timesin increments, the point of intersection can be stepped along the pipe or pipeline so that corrosion can be detected at various locations.
Also, there is a group of patents relating to detection of corrosion in pipelines, these being the following:
U.S. Pat. No. 4,839,593, U.S. Pat. No. 4,990,851, U.S. Pat. No. 4,929,898, and U.S. Pat. No. 4,926,986. Three of these issued to Brian R. Spies as inventor, and one to Pedro F. Lara as inventor. These patents deal with a transient electromagnetic method of detecting irregularities on container walls of pipelines by measuring wall thickness. Basically the inventors utilize transient electromagnetic probing called "TEMP", which allows the remote probing of a conductor by inducing a current into the conductor and analyzing the decay of current. It is the induced field with which these patents deal.
There is a fundamental difference between those four patents and the present invention. The method in those four patents is based completely on the quasi-static electromagnetic phenomenon, which is a different field and neglects the propagation field entirely with which the present patent application deals. It is stated that it is only the conductivity of the container which plays a role in the diffusion of induced field in the conductor, and they are measuring the decay of the induced diffusion field in the conductor.
The present invention fundamentally is completely different from the above mentioned four patents. The present invention deals with the complete dynamic electromagnetic phenomenon, which is about the dynamic aspects of electromagnetic wave propagation, reflection and refraction, and detraction, attenuation, dispersion, etc. It is the propagating field with which the present invention deals. The conductivity of the conductor is just one of the electromagnetic parameters. More importantly, the present invention deals with the permitivity which in essence controls the dynamic electromagnetic wave propagation. In the dynamic electromagnetic wave phenomenon, the conductivity enters into the attenuation of electromagnetic wave propagation, and the permitivity fundamentally governs the propagation field. Naturally, the present invention deals with permeability, and the permeability plays a role in both attenuation and propagation.
Other patents of possible interest will be cited in a prior art statement to be filed subsequently to the filing of the present application.
It is the object of the present invention to provide a means of inspecting pipes or pipelines under the in situ environments and circumstances that corrosion, and/or defects, and/or other anomalies can be detected with a relatively high degree of reliability, and that the various difficulties of inspection, such as those mentioned above, can be eliminated and/or alleviated.